A method for determining a suppression coefficient for suppressing noise on the basis of a phase difference in a plurality of sound signals input from a microphone array is known as a method for suppressing a noise component included in a sound signal picked up by a microphone. Further, with respect to this type of noise suppressing method, it is known that a vocalization interval is detected from a sound signal on the basis of a phase difference in a plurality of sound signals and that a method for determining a suppression coefficient is changed between a vocalization interval and a non-vocalization interval.
When a vocalization interval is detected from a sound signal, a phase difference area is set that includes a direction of a sound source as viewed from a microphone array, and it is determined whether the interval is a vocalization interval on the basis of an arrival rate of a sound that arrives from a direction of the phase difference area. The sound arrival rate is calculated on the basis of the phase difference area and a phase difference in each frequency band with respect to a plurality of sound signals. Whether the interval is a vocalization interval is determined according to whether the sound arrival rate is not less than a threshold. When it is determined whether the interval is a vocalization interval on the basis of the sound arrival rate, a time at which the sound arrival rate is changed from a value less than the threshold to a value not less than the threshold is a start time of a vocalization interval, and a time at which the sound arrival rate is changed from the value not less than the threshold to the value less than the threshold is a finish time of the vocalization interval.
Further, a method for reducing a false detection of a vocalization interval due to residual noise (a source error) by time-smoothing a sound arrival rate in a plurality of consecutive frames when it is determined whether the interval is a vocalization interval on the basis of the arrival rate is known (see, for example, Patent Document 1).
Document 1: Japanese Laid-open Patent Publication No. 2012-198289